Photocathodes as photoelectric conversion materials play a key role in vacuum photodetectors, accelerator-based light sources, and ultrafast electron microscopy. Since graphene has unique properties such as gas impermeability, electron transparency, a large specific surface area, and atomic thinness, the graphene/metal van der Waals heterojunction material may provide the possibility to improve the photoemission performance of metal photocathodes through surface modification. The specific Cs/O activation process was performed on the surface of graphene/copper heterojunction material. Its photoemission behaviors, including light-excited current, spectral response, and degradation characteristic, were investigated to verify the effect of surface modification on the improvement of photoemission performance. The experimental results show that, by preliminary Cs/O activation, the graphene/Cu photocathode can extend the threshold of spectral response to the near-infrared region. Furthermore, through repeated Cs/O activation, the cathode sample can possess better stability of operation. The photoelectron spectroscopy measurement results present the changes in the chemical states of surface elements and the corresponding work function after Cs/O activation and degradation. This Cs/O-activated graphene/metal photocathode can provide a new strategy to enhance the photoemission performance and stability of such photocathodes.
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